1. Field of the Invention
The invention concerns a process for the low-loss braking of an electrically driven vehicle with two electric motors connected in parallel and located one on each side of the vehicle, and which are controlled by pulse control.
2. Description of the Prior Art
Vehicles with drives of the said type have been braked by dynamic (or plug) braking up to now. The braking process is unleashed by the operator, e.g., by actuating the counterpedal in the case of two-pedal control, and by switching over the travel direction with a hand switch in the case of one-pedal control. Braking then occurs proportionally to the pedal position.
To produce a braking torque, a pole change is effected in the field exciting the electric motor by means of electric switchings or the direction of current through the electric motor is reversed.
In the case of dynamic braking, the two parallel-connected electric motors are switched over electrically in the opposite direction of rotation, while those of the wheels of the vehicle are still driven in the original direction of rotation. The armatures of the two motors are short-circuited by means of armature diodes and the energizing field is excited by current pulses by means of pulse control in order to generate a sufficiently high braking torque. The short-circuit current over the armature diode causes Joule losses at the internal resistance of each armature. Because the current strengths arising during the braking process are high in comparison with other driving modes and flow through the armature of each motor within a few seconds, a high heat generation occurs there due to Joule losses, which sharply reduces the service life of the electric motors.
The purpose of the present invention is thus to develop a braking process for vehicles with drives of the type described above, in which the Joule losses occurring and the associated disadvantages are minimized, and to provide a suitable arrangement for it.